In “Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access” (E-UTRA), single-carrier frequency division multiple access (SC-FDMA) is employed as an uplink radio access method. See, 3GPP TS 36.211, “E-UTRA; Physical Channels and Modulation (Release 8)” for the uplink radio access method.
In SC-FDMA, as exemplified in FIG. 1, mobile stations (or terminals, user devices, users, etc.; in this example, users A, B, C, D, and E) in a cell transmit signals using different time and frequency resources (the minimum unit of resources is called a resource block) to achieve orthogonality between the signals from the mobile stations. Also in SC-FDMA, a consecutive frequency band is allocated to each mobile station to achieve single-carrier transmission with a low peak-to-average power ratio (PAPR). This in turn makes it possible to reduce power consumption of the mobile stations and to provide wider coverage than multicarrier transmission. Allocation of time and frequency resources is determined by a scheduler of the base station based on propagation conditions of users and QoS (e.g., data rate, error rate, and/or delay) of data to be transmitted. This approach makes it possible to allocate time and frequency resources that provide good propagation conditions to respective users and thereby to increase the throughput.
In SC-FDMA, an uplink control channel is used to transmit a channel quality indicator (CQI) used for frequency scheduling and adaptive modulation and coding of a downlink data channel and to transmit acknowledgement information used for retransmission control of downlink data. The acknowledgement information is generated, for example, based on the result of error detection such as cyclic redundancy check (CRC). When no error is detected, acknowledge (ACK) is transmitted as the acknowledgement information; and when an error is detected, negative acknowledge (NACK) is transmitted as the acknowledgement information.